Infrared ear thermometry versus rectal thermometry in
children

The precise and accurate measurement of core temperature helps in the confirmation or
exclusion of fever. No routinely used site for core temperature is completely reliable for
estimating core temperature. The rectal route has traditionally been the reference standard
for measurement of core temperature,1-3 despite being uncomfortable and unpopular for
both patient and parents; the rectal site may also be slow to respond to rapidly changing
core temperatures.4

There is wide agreement between temperatures measured at the axilla, the rectum, and
the tympanic membrane, although temperatures taken from the tympanic membrane are
less accurate than those measured in the pulmonary artery.1,4 Milewski and colleagues4
showed that rectal temperatures in adults correlate more closely with pulmonary artery
readings than tympanic measurements, although others1 contend that tympanic
temperatures are more reflective of core temperatures than the temperatures obtained from
the rectal or axillary sites.1 Over the past 15 years, the use of infrared tympanic
thermometry has become more popular in both hospital and community practice with
about two-thirds of paediatricians and family-health physicians using tympanic
thermometers.5,6 Tympanic temperatures correlate well with temperatures taken
simultaneously from the oesophagus and rectum.1

Although many studies have attested to the reliability and popularity of tympanic
thermometry,7,8 other studies have expressed concerns about accuracy.9-11 Some
investigators showed that the tympanic temperatures differed from true rectal temperatures
by over 0·3ºC in between 26 and 62% of patients and by over 0·6ºC in about a third of
patients.7,11 The upper and lower limits of agreement between temperatures recorded at
the rectum and ear canal can be as wide as +3ºC and -1·2ºC in simultaneous recordings,7
while the corresponding variability for tympanic and axillary temperature was between
+2·49ºC and -0·74ºC.12 The ability of tympanic thermometry to detect or exclude pyrexia
ranged from 88·9% to 98·2%.7 It has also been suggested that there is need to exercise
caution in the use of the rectum as a reference standard, since the anatomical position of
the tympanic membrane is superior to the rectum because of the proximity of the
tympanic membrane to the blood bathing the hypothalamus which represents the true
core temperature.2

In this issue of The Lancet, Jean Craig and colleagues, in a systematic review, showed a
pooled mean difference between the rectal and tympanic temperatures of 0·29ºC (95% CI
-0·74 to 1·32). The investigators, however, conclude that infrared tympanic thermometry
does not show sufficient agreement with the other methods because of the wide variability
in measurement. The wide variability in these results implies false-high and false-low
temperatures, which will have serious implications for management because the readings
may lead to unjustified reassurance or unnecessary intervention. However, a recent study7
showed utility, accuracy, and reliability of tympanic thermometry, and few false-negative or
false-positive results with a smaller mean difference of -0·09ºC (0·13 to 0·05) and a high
concordance of 0·832 (0·801 to -0·864) between aural and rectal temperatures.

What should be the interpretation of the results so far? The wide variability between
studies and the poor degree of agreement in the systematic review by Craig and
colleagues between aural and rectal temperatures may be largely methodical. The
meta-analysis may have been affected by different methods in the studies, and it might
have been difficult to control for quality of instrumentation and technique. Although
tympanic thermometry is acceptable to patients, parents, and healthcare practitioners,13
it is not yet clear that tympanic thermometry is sufficiently accurate to measure core
temperature.9-11,14

Department of Paediatrics, College of Medicine, University College Hospital, Ibadan,
Nigeria (e-mail:asegun@hotmail.com)

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axillary, bladder, tympanic and pulmonary artery temperatures in children. J
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